The problem with an infinite regress or an infinite universe is that you would never arrive to 'now'. It is an impossibility since there is no starting point...no t=0 where time can accumulate from.
For example, pretend you have a train that is starting an infinite distance away from you. When will that train ever arrive at your location? Never. No matter how long it goes, it will never get to your location. That is what happens if you 'take the floor out' from under time.
Just like shooting a gun and trying to hit a target at infinity. When will it hit? Never.
For reasons like this, there is pretty much common consensus that the universe had a definite beginning. In fact, I believe it was Einstein who showed that time, space, matter, and energy must have come into being together at a single point.